Semiconductor devices having wireless communication functions for transmitting and receiving data wirelessly have been put into practical use in a variety of fields. Semiconductor devices having wireless communication functions have been expected as new communication information terminals, and the market of such semiconductor devices has been expected to become much larger. In semiconductor devices having wireless communication functions, which are put into practical use, antennas and integrated circuits formed using semiconductor elements are formed over the same substrates. Further, semiconductor devices having wireless communication functions are also referred to as wireless tags, RF (radio frequency) tags, RFID (radio frequency identification) tags, IC (integrated circuit) tags, or ID (identification) tags.
A semiconductor device having a wireless communication function can communicate with a wireless communication device which is a power supply source and a transmitting and receiving device (also referred to as an interrogator or a reader/writer). The structure of a conventional semiconductor device having a wireless communication function is described below with reference to a block diagram in FIG. 10.
The conventional semiconductor device having a wireless communication function (also simply referred to as a semiconductor device), which is illustrated in FIG. 10, includes an antenna 11, a rectifier circuit 12, a demodulation circuit 13, a constant voltage circuit 14, a logic circuit 15, and a modulation circuit 16. When the semiconductor device receives radio waves transmitted from a wireless communication device, AC voltage is generated in the internal antenna 11. The generated AC voltage is applied to the rectifier circuit 12 and the demodulation circuit 13. The AC voltage rectified in the rectifier circuit 12 is converted into DC voltage in the constant voltage circuit 14 and is applied to the logic circuit 15. The AC voltage is demodulated in the demodulation circuit 13, and a demodulated signal is input to the logic circuit 15. Analysis of the signal and generation of a response signal are performed in the logic circuit 15, and the response signal is output to the modulation circuit 16. The modulation circuit 16 performs load modulation on the antenna 11 by using the response signal, so that a signal is transmitted to the wireless communication device. Thus, wireless communication is performed between the semiconductor device and the wireless communication device.
In general, power supplied from a wireless communication device to a semiconductor device attenuates in proportion to the square of a distance between the semiconductor device and the wireless communication device (hereinafter referred to as a communication distance). That is, the amount of power supplied to the semiconductor device varies depending on the communication distance.
When the communication distance is long, the amount of power supplied to the semiconductor device is decreased. Needless to say, the level of DC voltage generated in accordance with the power is lowered, so that an integrated circuit cannot be operated. Therefore, in order to improve the communication distance, semiconductor devices which can generate desired drive power supply voltage even in the case where the communication distance is long have actively developed (for example, see Reference 1). Specifically, semiconductor devices which can amplify input signals have actively developed.